This invention concerns drives for agricultural machine elements and more particularly a variable speed drive especially useful for driving a harvesting machine element such as the threshing cylinder of a combine.
Variable speed drives for harvesting machine elements make it possible to adjust element speed to optimize performance in a particular operating condition or crop type. Thus, drive systems for combine harvester threshing cylinders commonly include a variable speed component such as an infinitely variable V-belt drive. Such drives, however, have an inherently limited speed range.
The speed range available is sometimes extended by including a changeable gear drive in the drive system so that the infinitely variable speed feature is available in two or more ranges. U.S. Pat. No. 3,375,738 Love, also assigned to the assignee of the present invention, discloses a drive of this general type. However, the geared portions of known drive systems were generally somewhat complex and bulky, particularly in terms of axial extent. Typically, even in co-axial gear-driven sheave arrangements, the driven sheave was axially and structurally separated from the final drive gear assembly. Manufacturing cost of such drives was relatively high and their bulk limited their adaptability.
The arrangement disclosed in co-pending patent application Ser. No. 299,277 filed Sept. 4, 1981 in the names of Love et al and also assigned to the assignee of the present invention, overcomes the above-mentioned problems. However, the embodiment there disclosed may, in some applications, suffer some shortcomings both in the direct drive and speed-reducing modes. In the direct drive mode, power is transmitted through the "locked up" epicyclic gear train with possibility of fretting or uneven wear on the gear teeth. In the speed-reducing mode, with the drive protected by a shear bolt arrangement, it is possible in some circumstances for damaging contact to occur between the adjacent parts disconnected by the shear bolt failure.